Field of the Invention
The present invention relates to a method for producing a fibroin-like protein using heterogeneous expression in Escherichia coli. 
Brief Description of the Related Art
Fibroin is a fibrous protein that is found in spider's thread and silkworm's thread. Spider's thread is a material that is four times stronger than steel, and tougher than carbon fiber and aramid fiber, and is highly elastic and heat resistant to heat. Therefore, the ability to conduct large-scale production of the constituents that make up these threads, such as fibroin or a fibrous proteins that are similar in structure to that of fibroin (henceforth generically referred to as “fibroin-like protein”).
As for the production of fibroin-like protein, heterogeneous expression thereof using Escherichia coli has been reported (WO2012/165476 and WO2006/008163).
It is also known that, in heterogeneous expression of proteins using Escherichia coli, the specific proliferation rate of bacterial cells correlates with the specific production rate of the heterogeneous protein. However, it has also been reported that, for example, the specific production rate of the TrpA1 protein in Escherichia coli is more greatly improved as the specific proliferation rate increases (R. Siegel and D. D. Y. Ryu, Biotechnol. Bioeng., 27:28-33 (1985)), whereas the specific production rate of β-lactamase in Escherichia coli is more greatly reduced as the specific proliferation rate increases (Seo, J.-H., Bailey, J. E., 1985b, Biotechnol. Bioeng., 27:1668-1674). Although the production amount of interferon α1 in Escherichia coli increases with reduced growth rate by glucose limitation, it is not influenced by phosphate limitation (Riesenberg D., Menzel K., Schulz V, Schumann K., Veith G., Zuber G., Knorre W. A., Appl. Microbiol. Biotechnol., 1990 October; 34(1):77-82). Furthermore, the yield of recombinant interferon α in Escherichia coli increases as the specific proliferation rate before inducing the expression increases (C. Curless, J. Pope, L. Tsai, Biotechnol. Prog., 1990, 6(2), pp. 149-152). Also, the expression amount of human growth hormone (hGH) in Escherichia coli is doubled by depletion of phosphate (Bech Jensen, E. and Carlsen, S., Biotechnol. Bioeng., 36:1-11, 1990). As described above, consistent relevance is not observed between the specific proliferation rate of cells or limitation of medium component, and the specific production rate of a heterogeneous protein.